In a delayed coking process, a heavy liquid hydrocarbon fraction is converted to solid coke, lower boiling hydrocarbon liquids, and gaseous products. The fraction is typically a residual petroleum based oil or a mixture of residual oil with other heavy fractions.
The residual oil is heated with liquid products from the process and is fed into a fractionating tower wherein light end products flashes from the residual oil. The oil is then pumped from the bottom of the fractionating tower through a furnace where it is heated to coking temperature and discharged into a coking drum.
In the coking reaction the residual feedstock is thermally decomposed into solid coke, condensable liquid, and gaseous hydrocarbons. The solid coke remains in the drum while hydrocarbon products are routed to the fractionating tower where they are separated into the desired hydrocarbon fractions.
The delayed coking drums must be vented prior to coke removal. This venting results in emission to the atmosphere. Among the emissions to the atmosphere is hydrogen sulfide which the Environmental Protection Agency has declared must be less than 10 tons per year. It is anticipated that this restriction may be reduced in the foreseeable future.